If

here we have to find the double derivative, so to find double derivative we will just differentiate the first derivative once again with a similar method.

Theorem: y and x are given in a different variable that is θ . We can find by finding and and then dividing them to get the required thing.

=

= 2cosθ – 2cos2θ ………..(1)

= -2sinθ + 2sin2θ ……….(2)

Dividing (1) and (2), we get

=

{as shown in question no. 18}

Let

⇒ To find f’’ we will differentiate f’ with θ and then divide with equation (2).

=

=

Now divide by equation (2).

Putting θ = π/2